The invention relates generally to a double overrunning clutch for use in power transmission devices and more particularly to an acceleration sensitive double overrunning clutch for use in motor vehicle drive lines.
The benefits of improved traction and vehicle control achieved by four-wheel drive systems in adverse driving and weather conditions such as snow, freezing rain, ice and even water has been known and appreciated by vehicle designers for many years. However, it is frequently argued that the weight and expense of providing an additional, secondary drive line having reliability equal to the primary drive line which is necessitated by its full time operation cannot be justified from the standpoint of the frequency such adverse driving conditions are encountered. These considerations often are satisfied by systems which operate part-time or on an as needed basis. Such systems may be significantly less rugged, weigh less and cost less inasmuch as they may be utilized only intermittently.
One of the less complex, part-time four wheel drive systems incorporates a simple mechanical one-way overrunning clutch between the primary drive line and secondary drive line. When the primary drive line attempts to overspeed the secondary drive line as will occur during an incipient skid caused by the application of drive torque exceeding the tire to road surface frictional coupling, the one-way clutch engages and transfers drive torque to the secondary drive wheels, thereby achieving four-wheel drive only under circumstances requiring it.
The use of a one way overrunning clutch to selectively provide drive torque to a secondary drive line upon primary wheel slip has not, however, become a popular solution to part-time four-wheel drive vehicles requirements and issues because of one problem: the clutch remains disengaged or inactive when reverse gear is selected unless, of course, the secondary drive line attempts to overspeed the primary drive line. Thus, in a situation frequently requiring four-wheel drive, that is, when the vehicle may need to be rocked or simply backed over terrain, a four-wheel drive configuration utilizing a one-way overrunning clutch will simply not provide four-wheel drive operation. This is a significant drawback of this clutch configuration.
One proposed solution to this difficulty comprehends the use of a double overrunning clutch. Here, a clutch configuration having a plurality of generally symmetrical roller receiving chambers formed by concentric drive and driven members also includes a cage and associated drag member which pre-stages or presets the roller in a forward or reverse direction. So staged or preset, the device functions to engage and release in response to drive or overrunning in the staged or preset direction, much as a one-way overrunning clutch would do. Operation, particularly engagement, of such double overrunning clutches, however, can be abrupt and questions have been raised with regard to customer satisfaction based upon occupant perception of clutch engagement and disengagement.
It is apparent, therefore, that improvements in the art of fully mechanical, selectively operating four-wheel drive systems utilizing double overrunning clutches are both desirable and possible.